The present invention relates to a magneto-optical recording medium in which the magnetically induced super-resolution technology is applied, and more particularly, to a magneto-optical recording/reproducing apparatus for such a magneto-optical recording medium.
To attain higher density of recording in a magneto-optical recording medium, magnetically induced super-resolution (MSR) technology has been proposed. With MSR technology the recording layer of a magneto-optical recording medium is formed from a minimum of three magnetic layers and magnetic switched coupling between the magnetic layers is utilized to assure a higher resolution than would be determined by the wavelength of a read light used.
MSR technology includes, for example, the FAD (front aperture detection) method in which the magnetic layer on the read light-irradiated side of a medium is magnetized in one direction in a high temperature area within a read light spot to detect signals from only a low temperature area, the RAD (rear aperture detection) method in which the magnetic layer on the read light-irradiated side is magnetized in one direction in a low temperature area within a read light spot to detect signals from only a high temperature area, the double-mask RAD method in which the magnetic layer on the read light-irradiated side is magnetized in one direction in the high and low temperature areas, respectively, within a read light spot to detect signals from only an intermediate temperature area between the high and low temperature areas, etc.
In all these methods, the area from which a signal is read by a read beam spot is narrow, which results in the same effect as would be obtained by reducing the size of the read beam spot. Therefore, it is possible to attain a higher density of recording in the magneto-optical recording medium than a resolution determined by the wavelength of a read light used.
To implement the above-mentioned MSR technology, when a read light is irradiated onto a magneto-optical recording medium to read information signals from the magneto-optical recording medium, it is necessary to apply a magnetic field to the magneto-optical recording medium in order to magnetize a part of the magneto-optical recording medium within a read light spot in one direction. The magnetic field will be referred to as xe2x80x9cread-head fieldxe2x80x9d hereinunder.
To enable use of MSR technology, the read-head field should desirably be reduced in strength. If a large read-head field has to be applied to enable the MSR technology, however, a magneto-optical recording/reproducing apparatus for use with the magneto-optical recording medium has to be provided with a special magnetic head which can apply such a large read-head field.
However, the magneto-optical recording apparatus basically comprises a writing magnetic head as a means for developing a magnetic field. When the read-head field may be small, the write head can be used to apply a read-head field.
Accordingly, the an object of the present invention is to overcome the above- mentioned drawbacks of the prior art by providing a magneto-optical recording medium in which MSR technology is applied and from which an information signal can be read with a small read-head field, and to provide a magneto-optical recording/reproducing apparatus adapted to read and write an information signal to/from such a magneto-optical recording medium.
The above object can be attained by providing a magneto-optical recording medium having:
a substrate having lands and grooves formed along a recording track; and
a recording layer formed on the substrate and consisting of a stack of at least three magnetic layers;
an information signal being written to the magneto-optical recording medium by the on-land recording method in which the information signal is written to the land; and
for reading the information signal from the magneto-optical recording medium, a magnetic field being applied to the magneto-optical recording medium so that a magnetic layer irradiated with a read light is magnetized in one direction in a part of the magnetic layer within a read light spot.
Because of the on-land recording method adopted, the MSR technology can be utilized to read an information signal from this magneto-optical recording medium with a smaller read-head field.
According to another aspect of the present invention, the magneto-optical recording medium should preferably be adapted such that when an information signal written on the magneto-optical recording medium is read, a read-head magnetic head is applied for the magnetic layer irradiated with a read light to be magnetized in predetermined directions in front and rear portions, respectively, lying in relation to the moving direction of the read light spot, of an area within the read light spot. In other words, the magneto-optical recording medium should preferably adopt the double-mask RAD method in the MSR technology. In the MSR technology, in particular, the double-mask RAD method attains a high resolution and thus permits to enable a higher density of recording in the magneto-optical recording medium.
According to another aspect of the present invention, the read-head field should preferably be 28,000 A/m or less in strength. The size of a magnetic field developed by a writing magnetic head provided in an ordinary magneto-optical recording/reproducing apparatus is on the order of 20,000 to 28,000 A/m. Therefore, by limiting the size of the read-head field to less than 28,000 A/m, it is possible to use the writing magnetic head as a magnetic head for application of a read-head field.
According to another aspect of the present invention, the magneto-optical recording medium should preferably be formed like a disc and have a plurality of recording bands defined by dividing a recording area thereof radially, the magneto-optical recording medium being spun at a predetermined speed with a write or read light focused within at least each of the recording bands when an information signal is written or read to/from the magneto-optical recording medium, the rotational speed or reference clock frequency being changed for each of the recording bands. In other words, the magneto-optical recording medium should preferably adopt the ZCAV (zone constant angular velocity) method. Adoption of the ZCAV method allows for an improved recording density without complicating the rotation drive circuitry of the magneto-optical recording/reproducing apparatus.
According to another aspect of the present invention, the magneto-optical recording medium should preferably be adapted such that when information signals written on the magneto-optical recording medium are read, a read-head magnetic head field is applied for the magnetic layer irradiated with a read light to be magnetized in predetermined directions in front and rear portions, respectively, lying in relation to the moving direction of the read light spot, of an area within the read light spot. In other words, the magneto-optical recording medium should preferably adopt the double-mask RAD method in the MSR technology. In the MSR technology, in particular, the double-mask RAD method attains a high resolution and thus permits to enable a higher density of recording in the magneto-optical recording medium.
According to another aspect of the present invention, to make the shortest recording pit length in the magneto-optical recording area smaller than that in the pit area, the shortest recording pit length in the pit area should preferably be an integral multiple of that in the magneto-optical recording area.
According to another aspect of the present invention, to make the shortest recording pit length in the magneto-optical recording area smaller than that in the pit area, the shortest recording pit length in the magneto-optical recording area should preferably be 0.38 xcexcm or less and the shortest recording pit length in the pit area be 0.76 xcexcm or less. Also, according to another aspect of the present invention, the track pitch should preferably be 0.9 xcexcm or less.
Currently, a 3.5-inch magneto-optical disc having a 640 MB capacity (conforming to ISO/IEC 15041; and referred to as xe2x80x9c5-fold density 3.5-inch magneto-optical discxe2x80x9d herein) has been developed. By designing a 3.5-inch magneto-optical disc in which the shortest recording pit length in the magneto-optical recording area is 0.38 xcexcm or less, that in the pit area is 0.76 xcexcm or less and track pitch is 0.9 xcexcm or less, it is possible to provide a 3.5-inch magneto-optical disc having a capacity two times larger than that of the 5-fold 3.5-inch magneto-optical disc, namely, provide a xe2x80x9c10-fold density 3.5-inch magneto-optical disc.xe2x80x9d
Also the above object can be attained by providing a magneto-optical recording/reproducing apparatus for writing and/or reading an information signal to/from a magneto-optical recording medium having a substrate with lands and grooves formed along a recording track; and a recording layer formed on the substrate and consisting of a stack of at least three magnetic layers, the apparatus being adapted, according to the present invention, to:
write an information signal to the magneto-optical recording medium by the on-land recording method in which the information signal is written to the land; and
apply a magnetic field to the magneto-optical recording medium when reading an information signal written on the magneto-optical recording medium; so that a magnetic layer irradiated with a read light is magnetized in one direction in a part of the magnetic layer within a read light spot. The magneto-optical recording/reproducing apparatus adopts the on-land recording method to permit reading of an information signal using MSR technology by applying a smaller read-head field.
According to another aspect of the present invention, the magneto-optical recording/reproducing apparatus should preferably comprises:
means for optimizing the strength of a magnetic field applied to the magneto-optical recording medium to read an information signal from the magneto-optical recording medium;
means for optimizing the intensity of a light irradiated to the magneto-optical recording medium to read the information signal from the magneto-optical recording medium; and
means for optimizing the intensity of a light irradiated to the magneto-optical recording medium to write an information signal to the magneto-optical recording medium. These means enable information signal write and read under optimum conditions.
According to another aspect of the present invention, the magneto-optical recording/reproducing apparatus should preferably be adapted such that when an information signal written on the magneto-optical recording medium is read, a read-head magnetic head is applied to the magnetic layer irradiated with a read light to be magnetized in predetermined directions in front and rear portions, respectively, lying in relation to the moving direction of the read light spot, of an area within the read light spot. In other words, the magneto-optical recording/reproducing apparatus should preferably adopt the double-mask RAD method in the MSR technology. With MSR technology, in particular, the double-mask RAD method attains a high resolution and thus permits to enable a higher density of recording in the magneto-optical recording medium.
According to another aspect of the present invention, the read-head field should preferably be 28,000 A/m or less in strength. The size of magnetic field developed by a writing magnetic head provided in an ordinary magneto-optical recording/reproducing apparatus is on the order of 20,000 to 28,000 A/m. Therefore, by limiting the size of the read-head field to less than 28,000 A/m, it is possible to use the writing magnetic head as a magnetic head for application of a read-head field.
According to another aspect of the present invention, the magneto-optical recording medium for use with the magneto-optical recording/reproducing apparatus should preferably be formed like a disc and have a plurality of recording bands defined by dividing a recording area radially thereof, the magneto-optical recording medium being spun at a predetermined speed with a write or read light focused within at least each of the recording bands when an information signal is written or read to/from the magneto-optical recording medium, the rotational speed or reference clock frequency being changed for each of the recording bands. In other words, the magneto-optical recording medium should preferably adopt the ZCAV (zone constant angular velocity) method. Adoption of the ZCAV method permits to improve the recording density without complicating the rotation drive circuitry of the magneto-optical recording/reproducing apparatus.
According to another aspect of the present invention, for use with a magneto-optical medium having a magneto-optical recording area in which an information signal is recorded by magneto-optical recording, and a pit area in which an information signal is pre-recorded by a convex-concave pattern, the magneto-optical recording/reproducing apparatus should preferably comprise:
means for generating a read clock corresponding to a recording pit length in the magneto-optical recording area; and
means for generating a read clock corresponding to a recording pit length in the pit area. These clock generating means permit normal write and/or read even when the recording pit length in the magneto-optical recording area is different from that in the pit area.
The provision of the above-mentioned magneto-optical recording area reading clock generating means and pit area reading clock generating means enables a magneto-optical recording/reproducing apparatus for use with a 10-fold density 3.5-inch magneto-optical recording medium in which the shortest recording pit length in the magneto-optical recording area is 0.38 xcexcm or less, that in the pit area is 0.76 xcexcm or less and track pitch is 0.9 xcexcm or less, for example.
These objects and other objects, features and advantages of the present intention will become more apparent from the following detailed description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings.